Antenna Toolkit

Antenna Toolkit 2nd Edition
Joseph J. Carr, K4IPV
Newnes
OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI
Newnes
An imprint of Butterworth-Heinemann
Linacre House, Jordan Hill, Oxford OX2 8DP
225 Wildwood Avenue, Woburn, MA 01801-2041
A division of Reed Educational and Professional Publishing Ltd
A member of the Reed Elsevier plc group
First published 1997
Reprinted 1998
Second edition 2001
ß Joseph J. Carr 1997, 2001
All rights reserved. No part of this publication
may be reproduced in any material form (including
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to some other use of this publication) without the
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Applications for the copyright holder’s written permission
to reproduce any part of this publication should be addressed
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British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library

ISBN 0 7506 4947 X
Typeset by Keyword Typesetting Services Ltd
Printed in Great Britain by
Preface vii
1. Radio signals on the move 1
2. Antenna basics 19
3. Wire, connection, grounds, and all that 49
4. Marconi and other unbalanced antennas 69
5. Doublets, dipoles, and other Hertzian antennas 87
6. Limited space antennas 118
7. Large loop antennas 129
8. Wire array antennas 153
9. Small loop antennas 176
10. Yagi beam antennas 195
11. Impedance matching 203
12. Simple antenna instrumentation and measurements 221
13. Getting a ‘good ground’ 237
Index 249
v
Contents

If you are interested in amateur radio, short-wave listening, scanner mon-
itoring, or any other radio hobby, then you will probably need to know a
few things about radio antennas. This book is intended for the radio enthu-
siast – whether ham operator, listening hobbyist, or radio science obser-
ver – who wants to build and use antennas for their particular
requirements and location. All of the antennas in this book can be made
from wire, even though it is possible to use other materials if you desire.
These antennas have several advantages. One of the most attractive is
that they can provide decent performance on the cheap. As one who has

lived through the experience of being broke, I learned early to use bits of
scrap wire to get on the air. My first novice antenna back in the late 1950s
was a real patched-together job – but it worked really well (or so I thought
at the time!).
Another advantage of wire antennas is that they are usually quite easy to
install. A couple of elevated supports (tree, roof, mast), a few meters of wire,
a few bits of radio hardware, and you are in the business of putting up an
antenna. As long as you select a safe location, then you should have little
difficulty erecting that antenna.
Finally, most high-frequency (HF) short-wave antennas are really easy to
get working properly. One does not need to be a rocket scientist – or pro-
fessional antenna rigger – to make most of these antennas perform as well
as possible with only a little effort. There is quite a bit of detailed technical
material to digest if you want to be a professional antenna engineer, but you
can have good results if you follow a few simple guidelines.
vii
Preface
SOFTWARE SUPPLEMENT TO THIS BOOK
_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
At the time this book was conceived it was noted that the technology now
exists to make Microsoft Windows-based antenna software available to
readers along with the book. The software can be used to calculate the
dimensions of the elements of most of the antennas in this book, as well
as a few that are not. There are also some graphics in the software that show
you a little bit about antenna hardware, antenna construction, and the like.
ANTENNA SAFETY
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Every time I write about antenna construction I talk a little bit about safety.
The issue never seems too old or too stale. The reason is that there seem to
be plenty of people out there who never get the word. Antenna erection does

not have to be dangerous, but if you do it wrong it can be very hazardous.
Antennas are deceptive because they are usually quite lightweight, and can
easily be lifted. I have no trouble lifting my trap vertical and holding it
aloft – on a windless day. But if even a little wind is blowing (and it almost
always is), then the ‘sail area’ of the antenna makes it a lot ‘heavier’ (or so it
seems). Always use a buddy-system when erecting antennas. I have a bad
back caused by not following my own advice.
Another issue is electrical safety. Do not ever, ever, ever toss an antenna
wire over the power lines. Ever. Period. Also, whatever type of antenna you
put up, make sure that it is in a location where it cannot possibly fall over
and hit the power line.
The last issue is to be careful when digging to lay down radials. You
really do not want to hit water lines, sewer lines, buried electrical service
lines, or gas lines. I even know of one property where a long-distance oil
pipeline runs beneath the surface. If you do not know where these lines are,
try to guess by looking at the locations of the meters on the street, and the
service entrance at the house. Hint: most surveyers’ plans (those map-like
papers you get at settlement) show the location of the buried services. They
should also be on maps held by the local government (although you might
have to go to two or three offices!. The utility companies can also help.
A NOTE ABOUT UNITS AND PRACTICES
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This book was written for an international readership, even though I am
American. As a result, some of the material is written in terms of US
standard practice. Wherever possible, I have included UK standard wire
sizes and metric units. Metric units are not in common usage in the USA,
but rather we still use the old English system of feet, yards, and inches.
Although many Americans (including myself) wish the USA would convert
to SI units, it is not likely in the near future. UK readers with a sense of
viii ANTENNA TOOLKIT

history might recognize why this might be true – as you may recall from the
George III unpleasantness, Americans do not like foreign rulers, so it is not
likely that our measuring rulers will be marked in centimeters rather than
inches.
*
For those who have not yet mastered the intricacies of converting
between the two systems:
1 inch ¼ 2:54 centimeters (cm) ¼ 25:4 millimeters (mm)
1 foot ¼ 30:48 cm ¼ 0:3048 meter (m)
1m ¼ 39:37 inches ¼ 3: 28 feet
Joseph J. Carr
PREFACE ix
*I apologize for the bad play on words, but I could not help it.

Anyone who does any listening to radio receivers at all – whether as a ham
operator, a short-wave listener, or scanner enthusiast – notices rather
quickly that radio signal propagation varies with time and something mys-
terious usually called ‘conditions.’ The rules of radio signal propagation are
well known (the general outlines were understood in the late 1920s), and
some predictions can be made (at least in general terms). Listen to almost
any band, and propagation changes can be seen. Today, one can find pro-
pagation predictions in radio magazines, or make them yourself using any of
several computer programs offered in radio magazine advertisements. Two
very popular programs are any of several versions of IONCAP, and a
Microsoft Windows program written by the Voice of America engineering
staff called VOACAP.
Some odd things occur on the air. For example, one of my favorite local
AM broadcast stations broadcasts on 630 kHz. During the day, I get inter-
ference-free reception. But after the Sun goes down, the situation changes
radically. Even though the station transmits the same power level, it fades

into the background din as stations to the west and south of us start skip-
ping into my area. The desired station still operates at the same power level,
but is barely audible even though it is only 20 miles (30 km) away.
Another easily seen example is the 3–30 MHz short-wave bands. Indeed,
even those bands behave very differently from one another. The lower-
frequency bands are basically ground wave bands during the day, and
become long-distance ‘sky wave’ bands at night (similar to the AM broad-
cast band (BCB)). Higher short-wave bands act just the opposite: during the
CHAPTER 1
Radio signals on the
move
1
day they are long-distance ‘skip’ bands, but some time after sunset, become
ground wave bands only.
The very high-frequency/ultra high-frequency (VHF/UHF) scanner
bands are somewhat more consistent than the lower-frequency bands.
But even in those bands sporadic-E skip, meteor scatter, and a number
of other phenomena cause propagation anomalies. In the scanner bands
there are summer and winter differences in heavily vegetated regions that
are attributed to the absorptive properties of the foliage. I believe I experi-
enced that phenomenon using my 2 m ham radio rig in the simplex mode
(repeater operation can obscure the effect due to antenna and location
height).
THE EARTH’S ATMOSPHERE
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Electromagnetic waves do not need an atmosphere in order to propagate, as
you will undoubtedly realize from the fact that space vehicles can transmit
radio signals back to Earth in a near vacuum. But when a radio wave does
propagate in the Earth’s atmosphere, it interacts with the atmosphere, and
its path of propagation is altered. A number of factors affect the interaction,

but it is possible to break the atmosphere into several different regions
according to their respective effects on radio signals.
The atmosphere, which consists largely of oxygen (O
2
) and nitrogen (N
2
)
gases, is broken into three major zones: the troposphere, stratosphere, and
ionosphere (Figure 1.1). The boundaries between these regions are not very
well defined, and change both diurnally (i.e. over the course of a day) and
seasonally.
The troposphere occupies the space between the Earth’s surface and an
altitude of 6–11 km. The temperature of the air in the troposphere varies
with altitude, becoming considerably lower at high altitude compared with
ground temperature. For example, a þ108C surface temperature could
reduce to À558C at the upper edges of the troposphere.
The stratosphere begins at the upper boundary of the troposphere
(6–11 km), and extends up to the ionosphere (%50 km). The stratosphere
is called an isothermal region because the temperature in this region is rela-
tively constant despite altitude changes.
The ionosphere begins at an altitude of about 50 km and extends up to
500 km or so. The ionosphere is a region of very thin atmosphere. Cosmic
rays, electromagnetic radiation of various types (including ultraviolet light
from the Sun), and atomic particle radiation from space (most of it from the
Sun), has sufficient energy to strip electrons away from the gas molecules of
the atmosphere. The O
2
and N
2
molecules that lost electrons are called

positive ions. Because the density of the air is so low at those altitudes, the
ions and electrons can travel long distances before neutralizing each other
2 ANTENNA TOOLKIT
by recombining. Radio propagation on some bands varies markedly
between daytime and night-time because the Sun keeps the level of ioniza-
tion high during daylight hours, but the ionization begins to fall off rapidly
after sunset, altering the radio propagation characteristics after dark. The
ionization does not occur at lower altitudes because the air density is such
that the positive ions and free electrons are numerous and close together, so
recombination occurs rapidly.
RADIO SIGNALS ON THE MOVE 3
FIGURE 1.1
PROPAGATION PATHS
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There are four major propagation paths: surface wave, space wave, tropo-
spheric, and ionospheric. The ionospheric path is important to medium-wave
and HF propagation, but is not important to VHF, UHF, or microwave
propagation. The space wave and surface wave are both ground waves, but
behave differently. The surface wave travels in direct contact with the
Earth’s surface, and it suffers a severe frequency-dependent attenuation
due to absorption into the ground.
The space wave is also a ground wave phenomenon, but is radiated from
an antenna many wavelengths above the surface. No part of the space wave
normally travels in contact with the surface; VHF, UHF, and microwave
signals are usually space waves. There are, however, two components of the
space wave in many cases: direct and reflected (Figure 1.2).
The ionosphere is the region of the Earth’s atmosphere that is between
the stratosphere and outer space. The peculiar feature of the ionosphere is
that molecules of atmospheric gases (O
2

and N
2
) can be ionized by stripping
away electrons under the influence of solar radiation and certain other
sources of energy (see Figure 1.1). In the ionosphere the air density is so
low that positive ions can travel relatively long distances before recombining
with electrons to form electrically neutral atoms. As a result, the ionosphere
remains ionized for long periods of the day – even after sunset. At lower
altitudes, however, air density is greater, and recombination thus occurs
rapidly. At those altitudes, solar ionization diminishes to nearly zero imme-
4 ANTENNA TOOLKIT
FIGURE 1.2
diately after sunset or never achieves any significant levels even at local
noon.
Ionization and recombination phenomena in the ionosphere add to the
noise level experienced at VHF, UHF, and microwave frequencies. The
properties of the ionosphere are therefore important at these frequencies
because of the noise contribution. In addition, in satellite communications
there are some transionospheric effects.
GROUND WAVE PROPAGATION
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The ground wave, naturally enough, travels along the ground, or at least in
close proximity to it (Figure 1.3).
There are two basic forms of ground wave: space wave and surface wave.
The space wave does not actually touch the ground. As a result, space wave
attenuation with distance in clear weather is about the same as in free space
(except above about 10 GHz, where absorption by H
2
O and O
2

increases
dramatically). Of course, above the VHF region, weather conditions add
attenuation not found in outer space.
The surface wave is subject to the same attenuation factors as the space
wave, but in addition it also suffers ground losses. These losses are due to
ohmic resistive losses in the conductive earth. Surface wave attenuation is a
function of frequency, and increases rapidly as frequency increases. For
both of these forms of ground wave, communications is affected by the
following factors: wavelength, height of both receive and transmit antennas,
distance between antennas, and terrain and weather along the transmission
path.
Ground wave communications also suffer another difficulty, especially at
VHF, UHF, and microwave frequencies. The space wave is like a surface
wave, but is radiated many wavelengths above the surface. It is made up of
RADIO SIGNALS ON THE MOVE 5
FIGURE 1.3
two components (see Figure 1.2): direct and reflected waves. If both of these
components arrive at the receive antenna they will add algebraically to
either increase or decrease signal strength. There is nearly always a phase
shift between the two components because the two signal paths have dif-
ferent lengths. In addition, there may be a 1808 ( radians) phase reversal at
the point of reflection (especially if the incident signal is horizontally polar-
ized).
Multipath phenomena exist because of interference between the direct
and reflected components of the space wave. The form of multipath phe-
nomenon that is, perhaps, most familiar to many readers (at least those old
enough to be ‘pre-cable’) is ghosting in television reception. Some multipath
events are transitory in nature (as when an aircraft flies through the trans-
mission path), while others are permanent (as when a large building or hill
reflects the signal). In mobile communications, multipath phenomena are

responsible for reception dead zones and ‘picket fencing.’ A dead zone exists
when destructive interference between direct and reflected (or multiple
reflected) waves drastically reduces signal strengths. This problem is most
often noticed at VHF and above when the vehicle is stopped; and the solu-
tion is to move the antenna a quarter wavelength. Picket fencing occurs as a
mobile unit moves through successive dead zones and signal enhancement
(or normal) zones, and sounds like a series of short noise bursts.
At VHF, UHF, and microwave frequencies the space wave is limited to
so-called ‘line of sight’ distances. The horizon is theoretically the limit of
communications distance, but the radio horizon is actually about 15%
further than the optical horizon. This phenomenon is due to refractive
bending in the atmosphere around the curvature of the Earth, and makes
the geometry of the situation look as if the Earth’s radius is four-thirds the
actual radius.
The surface wave travels in direct contact with the Earth’s surface, and it
suffers a severe frequency-dependent attenuation due to absorption by the
ground (Figure 1.3). The zone between the end of the ground wave and
where the sky wave touches down is called the skip zone, and is a region
of little or no signal. Because of this phenomenon, I have seen situations on
the 15 m band (21.390 MHz) where two stations 65 km apart (Baltimore,
Maryland, and Fairfax, Virginia) could not hear each other, and their com-
munications have to be relayed via a ham station in Lima, Peru!
The surface wave extends to considerable heights above the ground level,
although its intensity drops off rapidly at the upper end. The surface wave is
subject to the same attenuation factors as the space wave, but in addition it
also suffers ground losses. These losses are due to ohmic resistive losses in
the conductive earth, and to the dielectric properties of the Earth.
Horizontally polarized waves are not often used for surface wave commu-
nications because the Earth tends to short circuit the electrical (E) field
6 ANTENNA TOOLKIT

component. On vertically polarized waves, however, the Earth offers elec-
trical resistance to the E-field and returns currents to following waves. The
conductivity of the soil determines how much energy is returned.
IONOSPHERIC PROPAGATION
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Now let us turn our attention to the phenomena of skip communications as
seen in the short-wave bands, plus portions of the medium-wave and lower
VHF regions. Ionospheric propagation is responsible for intercontinental
broadcasting and communications.
Long-distance radio transmission is carried out on the HF bands
(3–30 MHz), also called the ‘short-wave’ bands. These frequencies are
used because of the phenomenon called skip. Under this type of propagation
the Earth’s ionosphere acts as if it is a ‘radio mirror,’ to reflect the signal
back to Earth. This signal is called the sky wave. Although the actual phe-
nomenon is based on refraction (not reflection, as is frequently believed) the
appearance to the casual ground observer is that short-wave and low-VHF
radio signals are reflected from the ionosphere as if it were a kind of radio
mirror. The actual situation is a little different, but we will deal with that
issue in a moment.
The key lies in the fact that a seeming radio mirror is produced by
ionization of the upper atmosphere. The upper portion of the atmosphere
is called the ‘ionosphere’ because it tends to be easily ionized by solar and
cosmic radiation phenomena. The reason for the ease with which that region
(50–500 km above the surface) ionizes is that the air density is very low.
Energy from the Sun strips away electrons from the outer shells of oxygen
and nitrogen molecules, forming free electrons and positive ions. Because
the air is so rarified at those altitudes, these charged particles can travel
great distances before recombining to form electrically neutral atoms again.
As a result, the average ionization level remains high in that region.
Several sources of energy will cause ionization of the upper atomosphere.

Cosmic radiation from outer space causes some degree of ionization, but the
majority of ionization is caused by solar energy. The role of cosmic radia-
tion was first noticed during World War II when military radar operators
discovered that the distance at which their equipment could detect enemy
aircraft was dependent upon whether or not the Milky Way was above the
horizon (although it was theorized 10 years earlier). Intergalactic radiation
raised the background microwave noise level, thereby adversely affecting the
signal-to-noise ratio.
The ionosphere is divided for purposes of radio propagation studies into
various layers that have different properties. These layers are only well
defined in textbooks, however, and even there we find a variation in the
height above the Earth’s surface where these layers are found. In addition,
RADIO SIGNALS ON THE MOVE 7
the real physical situation is such that layers do not have sharply defined
boundaries, but rather fade one into another. The division into layers is
therefore somewhat arbitrary. These layers (shown earlier in Figure 1.1)
are designated D, E, and F (with F being further subdivided into the F
1
and F
2
sublayers).
D-layer
The D-layer is the lowest layer in the ionosphere, and exists from approxi-
mately 50 to 90 km above the Earth’s surface. This layer is not ionized as
much as higher layers because all forms of solar energy that cause ionization
are severely attenuated by the higher layers above the D-layer. Another
reason is that the D-layer is much denser than the E- and F-layers, and
that density of air molecules allows ions and electrons to recombine to form
electroneutral atoms very quickly.
The extent of D-layer ionization is roughly proportional to the height of

the Sun above the horizon, so will achieve maximum intensity at midday.
The D-layer exists mostly during the warmer months of the year because of
both greater height of the sun above the horizon and the longer hours of
daylight. The D-layer almost completely disappears after local sunset,
although some observers have reported sporadic incidents of D-layer activ-
ity for a considerable time past sunset. The D-layer exhibits a large amount
of absorption of medium-wave and short-wave signals, to such an extent
that signals below 4–6 MHz are completely absorbed by the D-layer.
E-layer
The E-layer exists at altitudes between approximately 100 and 125 km.
Instead of acting as an attenuator it acts primarily as a reflector although
signals do undergo a degree of attenuation.
Like the D-layer, ionization in this region only exists during daylight
hours, peaking around midday and falling rapidly after sunset. After night-
fall the layer virtually disappears although there is some residual ionization
there during the night-time hours.
The distance that is generally accepted to be maximum that can be
achieved using E-layer propogation is 2500 km, although it is generally
much less than this and can be as little as 200 km.
One interesting and exciting aspect of this region is a phenomenon called
Es or sporadic E. When this occurs a layer or cloud of very intense ioniza-
tion forms. This can reflect signals well into the VHH region of the radio
spectrum. Although generally short lived, there can be openings on bands as
high as 2 meters (144 MHz). These may last as little as a few minutes, whilst
long openings may last up to a couple of hours. The phenomenon also
affects lower frequencies like the 10 meter and 6 meter amateur bands as
8 ANTENNA TOOLKIT
well as the VHF FM band. Sporadic E is most common in the summer
months, peaking in June (in the northern hemisphere). Distances of between
1000 and 2500 km can be reached using this mode of propagation.

F-layer
The F-layer of the ionosphere is the region that is the principal cause of
long-distance short-wave communications. This layer is located from about
150–500 km above the Earth’s surface. Unlike the lower layers, the air den-
sity in the F-layer is low enough that ionization levels remain high all day,
and decay slowly after local sunset. Minimum levels are reached just prior to
local sunrise. Propagation in the F-layer is capable of skip distances up to
4000 km in a single hop. During the day there are actually two identifiable,
distinct sublayers in the F-layer region, and these are designated the ‘F
l
’ and
‘F
2
’ layers. The F
1
layer is found approximately 150–250 km above the
Earth’s surface, while the F
2
layer is above the F
1
to the 450–500 km
limit. Beginning at local sundown, however, the lower regions of the F
1
layer begin to de-ionize due to recombination of positive ions and free
electrons. At some time after local sunset the F
1
and F
2
layers have
effectively merged to become a single reduced layer beginning at about

300 km.
The height and degree of ionization of the F
2
layer varies over the course
of the day, with the season of the year, and with the 27 day cycle of the sun.
The F
2
layer begins to form shortly after local sunrise, and reaches a max-
imum shortly before noon. During the afternoon the F
2
layer ionization
begins to decay in an exponential manner until, for purposes of radio pro-
pagation, it disappears sometime after local sunset. There is some evidence
that ionization in the F-layer does not completely disappear, but its impor-
tance to HF radio communication does disappear.
IONOSPHERIC VARIATION AND DISTURBANCES
_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
The ionosphere is an extremely dynamic region of the atmosphere, especially
from a radio operator’s point of view, for it significantly alters radio pro-
pagation. The dynamics of the ionosphere are conveniently divided into two
general classes: regular variation and disturbances. We will now look at both
types of ionospheric change.
Ionospheric variation
There are several different forms of variation seen on a regular basis in the
ionosphere: diurnal, 27 day (monthly), seasonal,and11 year cycle.
RADIO SIGNALS ON THE MOVE 9
Diurnal (daily) variation
The Sun rises and falls in a 24 hour cycle, and because it is a principal source
of ionization of the upper atmosphere, one can expect diurnal variation.
During daylight hours the E- and D-levels exist, but these disappear at

night. The height of the F
2
layer increases until midday, and then decreases
until evening, when it disappears or merges with other layers. As a result of
higher absorption in the E- and D-layers, lower frequencies are not useful
during daylight hours. On the other hand, the F-layers reflect higher
frequencies during the day. In the 1–30 MHz region, higher frequencies
(>11 MHz) are used during daylight hours and lower frequencies
(<11 MHz) at night. Figure 1.4B shows the number of sunspots per year
since 1700.
27 day cycle
Approximately monthly in duration, this variation is due to the rotational
period of the Sun. Sunspots (Figure 1.4A) are localized on the surface of the
Sun, so will face the Earth only during a portion of the month. As new
sunspots are formed, they do not show up on the earthside face until their
region of the Sun rotates earthside.
Seasonal cycle
The Earth’s tilt varies the exposure of the planet to the Sun on a seasonal
basis. In addition, the Earth’s yearly orbit is not circular, but elliptical. As a
result, the intensity of the Sun’s energy that ionizes the upper atmosphere
varies with the seasons of the year. In general, the E-, D-, and F-layers are
affected, although the F
2
layer is only minimally affected. Ion density in the
F
2
layer tends to be highest in winter, and less in summer. During the
summer, the distinction between F
1
and F

2
layers is less obvious.
10 ANTENNA TOOLKIT
FIGURE 1.4A
11 year cycle
The number of sunspots, statistically averaged, varies on an approximately
11 year cycle (Fig. 1.4B). As a result, the ionospheric effects that affect radio
propagation also vary on an 11 year cycle. Radio propagation in the short-
wave bands is best when the average number of sunspots is highest. Peaks
occurred in 1957, 1968, 1979, and 1990.
Events on the surface of the Sun sometimes cause the radio mirror to seem
almost perfect, and make spectacular propagation possible. At other times,
however, solar disturbances disrupt radio communications for days at a time.
There are two principal forms of solar energy that affect short-wave
communications: electromagnetic radiation and charged solar particles.
Most of the radiation is beyond the visible spectrum, in the ultraviolet
and X-ray/-ray region of the spectrum. Because electromagnetic radiation
travels at the speed of light, solar events that release radiation cause changes
to the ionosphere about 8 minutes later. Charged particles, on the other
hand, have a finite mass and so travel at a considerably slower velocity.
They require 2 or 3 days to reach the Earth.
Various sources of both radiation and particles exist on the Sun. Solar
flares may release huge amounts of both radiation and particles. These
events are unpredictable and sporadic. Solar radiation also varies over an
approximately 27 day period, which is the rotational period of the Sun. The
same source of radiation will face the Earth once every 27 days, so events
tend to be somewhat repetitive.
RADIO SIGNALS ON THE MOVE 11
FIGURE 1.4B
Solar and galactic noise affect the reception of weak signals, while solar

noise will also either affect radio propagation or act as a harbinger of
changes in propagation patterns. Solar noise can be demonstrated by
using an ordinary radio receiver and a directional antenna, preferably oper-
ating in the VHF/UHF regions of the spectrum. If the antenna is aimed at
the Sun on the horizon at either sunset or sunrise a dramatic change in
background noise will be noted as the Sun slides across the horizon.
Sunspots
A principal source of solar radiation, especially the periodic forms, is sun-
spots (Figure 1.4A). Sunspots can be as large as 100 000–150 000 km in
diameter, and generally occur in clusters. The number of sunspots varies
over a period of approximately 11 years, although the actual periods since
1750 (when records were first kept) have varied from 9 to 14 years (Fig.
1.4B). The sunspot number is reported daily as the statistically massaged
Zurich smoothed sunspot number,orWolf number. The number of sunspots
greatly affects radio propagation via the ionosphere. The low was in the
range of 60 (in 1907), while the high was about 200 (1958).
Another indicator of ionospheric propagation potential is the solar flux
index (SFI). This measure is taken in the microwave region (wavelength of
10.2 cm, or 2.8 GHz), at 1700 U.T. Greenwich Mean Time in Ottawa,
Canada. The SFI is reported by the National Institutes of Standards and
Technology (NIST) radio stations WWV (Fort Collins, Colorado) and
WWVH (Maui, Hawaii).
The ionosphere offers different properties that affect radio propagation
at different times. Variations occur not only over the 11 year sunspot cycle
but also diurnally and seasonally. Obviously, if the Sun affects propagation
in a significant way, then differences between night-time and daytime, and
between summer and winter, must cause variations in the propagation
phenomena observed.
Ionospheric disturbances
Disturbances in the ionosphere can have a profound effect on radio com-

munications – and most of them (but not all) are bad. In this section we will
briefly examine some of the more common forms.
Sporadic E-layer
A reflective cloud of ionization sometimes appears in the E-layer of the
ionosphere; this layer is sometimes called the E
s
layer. It is believed that
the E
s
layer forms from the effects of wind shear between masses of air
moving in opposite directions. This action appears to redistribute ions
into a thin a layer that is radio-reflective.
12 ANTENNA TOOLKIT
Sporadic-E propagation is normally thought of as a VHF phenomenon,
with most activity between 30 and 100 MHz, and decreasing activity up to
about 100 MHz. However, about 25–50% of the time, sporadic-E propaga-
tion is possible on frequencies down to 10–15 MHz. Reception over paths of
2300–4200 km is possible in the 50 MHz region when sporadic-E propaga-
tion is present. In the northern hemisphere, the months of June and July are
the most prevalent sporadic-E months. On most days when the sporadic-E
phenomenon is present it lasts only a few hours.
Sudden ionospheric disturbances (SIDs)
The SID, or ‘Dellinger fade,’ mechanism occurs suddenly, and rarely gives
any warning. Solar flares (Figure 1.5) are implicated in SIDs. The SID may
last from a few minutes to many hours. It is believed that SIDs occur in
correlation with solar flares or ‘bright solar eruptions’ that produce
immense amounts of ultraviolet radiation that impinge the upper atmo-
sphere. The SID causes a tremendous increase in D-layer ionization,
which accounts for the radio propagation effects. The ionization is so
intense that all receiver operators on the sunny side of the Earth experience

profound loss of signal strength above about 3 MHz. It is not uncommon
for receiver owners to think that their receivers are malfunctioning when this
RADIO SIGNALS ON THE MOVE 13
FIGURE 1.5
occurs. The sudden loss of signal by sunny-side receivers is called Dellinger
fade. The SID is often accompanied by variations in terrestial electrical
currents and magnetism levels.
An interesting anomaly is seen when SIDs occur. Although short-wave
reception is disrupted, and may stay that way for awhile, distant very low-
frequency (VLF) signals, especially in the 15–40 kHz region, experience a
sudden increase in intensity. This is due to the fact that the SID event
results in deep ionization way into the D-layer. This ionization increases
absorption of HF signals. But the wavelength of VLF signals is close to
the distance from the Earth’s surface to the bottom of the D-layer, so that
space acts like a gigantic ‘waveguide’ (as used in the transmission of
microwaves) when the SID is present – thus propagating the VLF signal
very efficiently.
Ionospheric storms
The ionospheric storm appears to be produced by an abnormally large rain
of atomic particles in the upper atmosphere, and is often preceded by a SID
18–24 hours earlier. These storms tend to last from several hours to a week
or more, and are often preceded by 2 days or so by an abnormally large
collection of sunspots crossing the solar disk. They occur most frequently,
and with greatest severity, in the higher latitudes, decreasing toward the
Equator. When the ionospheric storm commences, short-wave radio signals
may begin to flutter rapidly and then drop out altogether. The upper iono-
sphere becomes chaotic, turbulence increases, and the normal stratification
into ‘layers’ or zones diminishes.
Radio propagation may come and go over the course of the storm, but it
is mostly absent. The ionospheric storm, unlike the SID which affects the

sunny side of the Earth, is worldwide. It is noted that the maximum usable
frequency (MUF) and critical frequency tend to reduce rapidly as the storm
commences.
An ionospheric disturbance observed over November 12–14, 1960 was
preceded by about 30 minutes of extremely good, but abnormal propaga-
tion. At 15.00 hours EST, European stations were noted in North America
with S9+ signal strengths in the 7000–7300 kHz region of the spectrum,
which is an extremely rare occurrence. After about 30 minutes, the bottom
dropped out, and even AM broadcast band skip (later that evening) was
non-existent. At the time, WWV was broadcasting a ‘W2’ propagation
prediction at 19 and 49 minutes after each hour. It was difficult to hear
even the 5 MHz WWV frequency in the early hours of the disturbance, and
it disappeared altogether for the next 48 hours. Of course, as luck would
have it, that event occurred during the first weekend of the ARRL
Sweepstakes ham radio operating contest that year.
14 ANTENNA TOOLKIT
GREAT CIRCLE PATHS
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A great circle is a line between two points on the surface of a sphere that lies
on a plane through the sphere’s center. When translated to ‘radio speak,’ a
great circle is the shortest path on the surface of the Earth between two
points. Navigators and radio operators use the great circle for similar, but
different reasons: the navigator in order to get from here to there, and the
radio operator to get a transmission path from here to there.
The heading of a directional antenna is normally aimed at the receiving
station along its great circle path. Unfortunately, many people do not
understand the concept well enough, for they typically aim the antenna in
the wrong direction. Radio waves do not travel along what appears to be the
best route on a flat map. Instead they travel along the shortest distance on a
real globe.

Long path versus short path
The Earth is a sphere (or more precisely, an ‘oblique spheroid’), so from
any given point to any other point there are two great circle paths: the
long path (major arc) and short path (minor arc). In general, the best
reception occurs along the short path. In addition, short-path propagation
is more nearly ‘textbook’ compared with long-path reception. However,
there are times when the long path is better, or is the only path that will
deliver a signal to a specific location from the geographic location in
question.
USING THE IONOSPHERE
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The refraction of HF and some medium-wave radio signals back to Earth
via the ionosphere gives rise to intercontinental HF radio communications.
This phenomenon becomes possible during daylight hours, and for a while
after sunset when the ionosphere is ionized. Figure 1.6 reiterates the
mechanism of long-distance skip communications. The transmitter is
located at point T, while receiving stations are located at sites R1 and R2.
Signals 1 and 2 are not refracted sufficiently to be returned to Earth, so they
are lost in space. Signal 3, however, is refracted enough to return to Earth,
so it is heard at station Rl. The skip distance for signal 3 is the distance from
T to Rl. At points between T and R1, signal 3 is inaudible, except within
ground wave distance of the transmitter site (T). This is the reason why two
stations 50 km apart hear each other only weakly, or not at all, while both
stations can communicate with a third station 3000 km away. In American
amateur radio circles it is common for South American stations to relay
between two US stations only a few kilometers apart.
RADIO SIGNALS ON THE MOVE 15